Eur Respir J 2005; 26: 511–522
DOI: 10.1183/09031936.05.00035005
CopyrightßERS Journals Ltd 2005
SERIES ‘‘ATS/ERS TASK FORCE: STANDARDISATION OF LUNG
FUNCTION TESTING’’
Edited by V. Brusasco, R. Crapo and G. Viegi
Number 3 in this Series
Standardisation of the measurement of
lung volumes
J. Wanger, J.L. Clausen, A. Coates, O.F. Pedersen, V. Brusasco, F. Burgos,
R. Casaburi, R. Crapo, P. Enright, C.P.M. van der Grinten, P. Gustafsson,
J. Hankinson, R. Jensen, D. Johnson, N. MacIntyre, R. McKay, M.R. Miller,
D. Navajas, R. Pellegrino and G. Viegi
CONTENTS
Background and purpose . . . . . . . . . . . . . . . . . . . . . . . . .
Definitions and subdivisions of lung volume . . . . . . . . . . .
Patient preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Derivation of lung subdivisions . . . . . . . . . . . . . . . . . . . . .
Measurement of FRC using body plethysmography . . . . .
Introduction and theory . . . . . . . . . . . . . . . . . . . . . . . . . . .
Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Measurement technique . . . . . . . . . . . . . . . . . . . . . . . . . .
Quality control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Measurement of FRC using nitrogen washout. . . . . . . . . .
Introduction and theory . . . . . . . . . . . . . . . . . . . . . . . . . . .
Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Measurement technique . . . . . . . . . . . . . . . . . . . . . . . . . .
Quality control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Measurement of FRC using helium dilution. . . . . . . . . . . .
Introduction and theory . . . . . . . . . . . . . . . . . . . . . . . . . . .
Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Measurement technique . . . . . . . . . . . . . . . . . . . . . . . . . .
Quality control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Measurement of lung volumes using imaging techniques.
Conventional radiographs . . . . . . . . . . . . . . . . . . . . . . . . .
Computed tomography . . . . . . . . . . . . . . . . . . . . . . . . . . .
Magnetic resonance imaging . . . . . . . . . . . . . . . . . . . . . . .
Controversies and critical questions . . . . . . . . . . . . . . . . . .
Reference values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Infection control. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Abbreviations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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AFFILIATIONS
For affiliations, please see
Acknowledgements section
CORRESPONDENCE
V. Brusasco
Internal Medicine
University of Genoa
V.le Benedetto XV, 6
I-16132 Genova
Italy
Fax: 39 0103537690
E-mail: vito.brusasco@unige.it
Received:
March 23 2005
Accepted after revision:
April 05 2005
KEYWORDS: Helium, lung function, lung physiology, lung volume measurements, nitrogen,
radiology
Previous articles in this series: No. 1: Miller MR, Crapo R, Hankinson J, et al. General considerations for lung function testing. Eur Respir J 2005; 26:
153–161. No. 2: Miller MR, Hankinson J, Brusasco V, et al. Standardisation of spirometry. Eur Respir J 2005; 26: 319–338.
EUROPEAN RESPIRATORY JOURNAL
VOLUME 26 NUMBER 3
European Respiratory Journal
Print ISSN 0903-1936
Online ISSN 1399-3003
c
511
STANDARDISATION OF LUNG VOLUME MEASUREMENT
J. WANGER ET AL.
BACKGROUND AND PURPOSE
Inspired and expired lung volumes measured by spirometry
are useful for detecting, characterising and quantifying the
severity of lung disease. Measurements of absolute lung
volumes, residual volume (RV), functional residual capacity
(FRC) and total lung capacity (TLC) are technically more
challenging, which limits their use in clinical practice. The role
of lung volume measurements in the assessment of disease
severity, functional disability, course of disease and response
to treatment remains to be determined in infants, as well as in
children and adults. Nevertheless, in particular circumstances,
measurements of lung volume are strictly necessary for a
correct physiological diagnosis [1].
In contrast to the relative simplicity of spirometric volumes, a
variety of disparate techniques have been developed for the
measurement of absolute lung volumes. These include the
following: body plethysmography (using various methodologies), nitrogen washout, gas dilution, and radiographic
imaging methods.
The present document integrates and consolidates the recommendations of the current American Thoracic Society (ATS)/
European Respiratory Society Task Force on pulmonary
function standards, and the recommendations from an earlier
National Heart, Lung, and Blood Institute (NHLBI) workshop
convened by the ATS. The NHLBI workshop participants, who
were experts with considerable adult and paediatric experience, published their input in the form of background papers
in the European Respiratory Journal between 1995 and 1999 [2–
12]. Later, a NHLBI workshop consensus document was
written, which can be found on the ATS website [13], for
those who require more in-depth descriptions, discussion and
a fuller derivation of equations.
DEFINITIONS AND SUBDIVISIONS OF LUNG VOLUME
The term ‘‘lung volume’’ usually refers to the volume of gas
within the lungs, as measured by body plethysmography, gas
dilution or washout. In contrast, lung volumes derived from
conventional chest radiographs are usually based on the
volumes within the outlines of the thoracic cage, and include
the volume of tissue (normal and abnormal), as well as the
lung gas volume. Lung volumes derived from computed
tomography (CT) scans can include estimates of abnormal lung
tissue volumes, in addition to normal lung tissue volumes and
the volume of gas within the lungs. In this statement,
previously accepted definitions will be used (fig. 1) [14–18].
The FRC is the volume of gas present in the lung at endexpiration during tidal breathing.
The expiratory reserve volume (ERV) is the volume of gas that
can be maximally exhaled from the end-expiratory level
during tidal breathing (i.e. from the FRC).
The maximum volume of gas that can be inspired from FRC is
referred to as the inspiratory capacity (IC).
The inspiratory reserve volume is the maximum volume of gas
that can be inhaled from the end-inspiratory level during tidal
breathing.
RV refers to the volume of gas remaining in the lung after
maximal exhalation (regardless of the lung volume at which
exhalation was started).
512
VOLUME 26 NUMBER 3
IRV
IC
IVC
VT
TLC
ERV
FRC
RV
FIGURE 1.
Static lung volumes and capacities based on a volume–time
spirogram of an inspiratory vital capacity (IVC). IRV: inspiratory reserve volume; VT:
tidal volume (TV); ERV: expiratory reserve volume; RV: residual volume; IC:
inspiratory capacity; FRC: functional residual capacity; TLC: total lung capacity.
The volume of gas inhaled or exhaled during the respiratory
cycle is called the tidal volume (TV or VT).
The thoracic gas volume (TGV or VTG) is the absolute volume
of gas in the thorax at any point in time and any level of
alveolar pressure. Since this term is too nonspecific, it is
recommended that its use should be discontinued and
replaced with more specific terminology, for example,
plethysmographic lung volume (abbreviated at VL,pleth), and
FRC by body plethysmography or TGV at FRC (FRCpleth).
TLC refers to the volume of gas in the lungs after maximal
inspiration, or the sum of all volume compartments.
The vital capacity (VC) is the volume change at the mouth
between the positions of full inspiration and complete
expiration. The measurement may be made in one of the
following ways: 1) inspiratory vital capacity (IVC), where the
measurement is performed in a relaxed manner, without
undue haste or deliberately holding back, from a position of
full expiration to full inspiration; 2) expiratory vital capacity
(EVC), where the measurement is similarly performed from a
position of full inspiration to full expiration; or 3) forced vital
capacity, which is the volume of gas that is exhaled during a
forced expiration, starting from a position of full inspiration
and ending at complete expiration.
PATIENT PREPARATION
Guidelines for patient preparation are included in the
statement on general considerations for lung function testing
in this series of documents [19].
DERIVATION OF LUNG SUBDIVISIONS
No matter what technique is used to measure FRC (see sections
entitled Measurement of FRC using body plethysmography,
Measurement of FRC using nitrogen washout, and
Measurement of FRC using helium dilution), two subdivisions
of the VC (IC and ERV) will have to be measured in order to
calculate the TLC and RV (fig. 1). It has proved difficult to
reach a consensus on whether the RV should be the minimal
value as would most probably be obtained by performing the
ERV manoeuvre from FRC and then subtracting ERV from the
measured value for FRC, or the approaches which would likely
result in higher RVs in those with obstructive lung disease
EUROPEAN RESPIRATORY JOURNAL
J. WANGER ET AL.
STANDARDISATION OF LUNG VOLUME MEASUREMENT
when RV was defined from either slow or forced expirations
starting from the point of maximal inspiration. It was also
difficult to identify a single method for measuring RV and TLC
that was efficient for clinical use and performable by those
with severe obstructive lung disease. While future studies are
needed to provide better scientific rationale, two methods are
recommended for computations of related lung volumes once
FRC has been determined.
The first and preferred method is to measure ERV immediately
after the acquisition of the FRC measurement(s), followed by
slow IVC manoeuvres, all performed as ‘‘linked’’ manoeuvres
(i.e. without the patient coming off the mouthpiece prior to the
completion of the manoeuvres; fig. 2). The reported value for
the FRC is the mean of the technically satisfactory FRC
measurements, linked to the technically satisfactory ERV and
IVC manoeuvres used for calculating the RV and TLC. The
reported value for RV is the reported value for FRC minus the
mean of the technically acceptable ERV measurements, linked
to technically acceptable FRC determinations. The reported
value of TLC is the reported value for RV plus the largest of the
technically acceptable IVCs.
The second recommended method utilises the performance of
IC manoeuvres immediately after the acquisition of the FRC
measurement(s) to measure the TLC. This method may be
necessary in those with severe obstructive dysfunction or
severe dyspnoea who are unable to follow the FRC measurements with a linked ERV manoeuvre as a result of dyspnoea.
The patients may come off the mouthpiece between successive
linked FRC and IC determinations, and also between the
separate VC manoeuvres that are required to calculate RV as
the mean TLC minus the largest VC measured. The VC
measurement can be derived from either the IVC manoeuvre
that follows an ERV manoeuvre (as used in the first method),
or from a slow EVC that follows an IC manoeuvre after the
Volume
IC
IRV
VT
FRC
ERV
RV
Quiet
breathing
Shutter
closed
Shutter
open
Time
FRC determination. The slow EVC can be linked with the
FRC/IC measurements if patient discomfort does not preclude
optimal performance. The reported value for the FRC is the
mean of technically acceptable FRC measurements used for the
calculation of TLC. The TLC is the mean of the three largest
sums of technically acceptable FRC values and linked IC
manoeuvres.
Recommendations for the measurement of VC are presented in
the document on the standardisation of spirometry in this
series [20]. There is insufficient evidence regarding optimal
recommendations for the reproducibility criteria of the ERV
and IC, which are used in computing TLC and RV.
The determination of FRC is the key component in the
measurement of lung volumes, and can be assessed by body
plethysmography, gas washout or gas dilution methods, or
using radiography. The FRCpleth includes nonventilated, as
well as ventilated, lung compartments, and, thus, yields higher
results than the gas dilution or washout methods [3, 11]. The
FRCpleth may be further increased by gas that is present in the
abdomen. In cases of severe airflow obstruction, FRCpleth may
be overestimated when panting rates are .1 Hz [21]. In
patients with severe airflow obstruction or emphysema, the
true value of the FRC is underestimated by the gas dilution or
washout methods. Despite this fact, the gas dilution/washout
methods are widely used because they are simple to perform
and the instrumentation is relatively inexpensive.
MEASUREMENT OF FRC USING BODY
PLETHYSMOGRAPHY
Introduction and theory
The term TGV (or VTG) refers to the plethysmographic
measurement of intrathoracic gas at the time of airflow
occlusion. The volume is the compressible gas within the
thorax. The term FRCpleth refers to the volume of intrathoracic
gas measured when airflow occlusion occurs at FRC.
In healthy individuals, there are usually minimal differences in
FRC measured by gas dilution/washout techniques and
plethysmography. However, in patients with lung disease
associated with gas trapping, most, but not all, studies indicate
that FRCpleth often exceeds the FRC measured by gas dilution
[3, 11].
Plethysmographic measurements are based on Boyle’s Law,
which states that, under isothermal conditions, when a
constant mass of gas is compressed or decompressed, the gas
volume decreases or increases and gas pressure changes such
that the product of volume and pressure at any given moment
is constant [11, 22]. More detailed reviews of the theory are
available [11, 13].
volume.
Equipment
The changes in thoracic volume that accompany a compression
or decompression of the gas in the lungs during respiratory
manoeuvres can be obtained using a body plethysmograph by
measuring the changes in the following: 1) pressure within a
constant-volume chamber (variable-pressure plethysmograph);
2) volume within a constant-pressure chamber (volumedisplacement plethysmograph); or 3) airflow in and out of a
constant-pressure chamber (flow plethysmograph). A flow
plethysmograph can be converted into a variable-pressure
EUROPEAN RESPIRATORY JOURNAL
VOLUME 26 NUMBER 3
FIGURE 2.
Volume–time display showing the sequence of quiet breathing and
after stable end-expiratory level is achieved, a short period when the shutter is
closed for determination of the thoracic gas volume, followed by an open-shutter
period during which the patient stays on the mouthpiece and performs an expiratory
reserve volume (ERV) manoeuvre followed by a slow inspiratory vital capacity
manoeuvre. All volumes are determined without the patient coming off the
mouthpiece, in a ‘‘linked’’ manoeuvre. IC: inspiratory capacity; FRC: functional
residual capacity; IRV: inspiratory reserve volume; VT: tidal volume (TV); RV: residual
513
c
STANDARDISATION OF LUNG VOLUME MEASUREMENT
Regardless of the plethysmograph type, a transducer capable
of measuring mouth pressure o¡5 kPa (o¡50 cmH2O), with
a flat frequency response in excess of 8 Hz, is essential.
Spirometers or pneumotachographs that are used for the
measurement of lung volumes and forced inspiratory and
expiratory volumes should meet published standards for the
accuracy and frequency response of spirometric devices [16,
23]. The transducer measuring changes in the chamber
pressure must be capable of accurately measuring a range of
¡0.02 kPa (¡0.2 cmH20) [16]. Thermal drift may give rise to a
pressure change of as much as 1.0 kPa (10 cmH20), which may
necessitate a larger working range of the transducer. A time
constant of 10 s for a controlled leak (which minimises slowly
occurring pressure changes) is ideal.
Thermal drift due to temperature changes in the interior of the
plethysmograph is common to all types of equipment, and can
be detected and compensated for from the volume–pressure
plot during an occlusion showing a systematic difference in
slope between compression and expansion [11]. A second
approach for compensation is to use an iterative method [24].
Manufacturers should state the frequency response of their
plethysmographic systems and provide instructions for the
user on how to verify it. The verification of frequency response
is most commonly accomplished by the application of a
sinusoidal volume signal, where the frequency can be varied
[11]. It is generally recommended that the minimum adequate
frequency response should be five times the frequency of the
signal being measured. For a pant at 1 Hz, this means fidelity
of the signal at 5 Hz. To ensure that panting frequencies
slightly above 1 Hz will not lead to problems, the minimum
acceptable frequency response should result in accuracy at
8 Hz.
Measurement technique
The measurement technique should adhere to the following
steps. 1) The equipment should be turned on and allowed an
adequate warm-up time. 2) The equipment is set up for testing,
including calibration, according to manufacturer’s instructions.
3) The equipment is adjusted so that the patient can sit
comfortably in the chamber and reach the mouthpiece without
having to flex or extend the neck. 4) The patient is seated
comfortably, with no need to remove dentures. The procedure
is explained in detail, including that the door will be closed,
the patient’s cheeks are to be supported by both hands, and a
nose clip is to be used. 5) The plethysmograph door is closed,
and time is allowed for the thermal transients to stabilise and
the patient to relax. 6) The patient is instructed to attach to the
mouthpiece and breathe quietly until a stable end-expiratory
level is achieved (usually 3–10 tidal breaths). 7) When the
patient is at or near FRC, the shutter is closed at end-expiration
for ,2–3 s, and the patient is instructed to perform a series
of gentle pants (,¡1 kPa (,¡10 cmH2O)) at a frequency
between 0.5 and 1.0 Hz [21, 25]. Panting frequencies of
.1.5 Hz may lead to errors, and those ,0.5 Hz may cause
problems with the controlled leak of the body plethysmograph
system. A metronome can be used to assist patients with this
514
VOLUME 26 NUMBER 3
manoeuvre. 8) A series of 3–5 technically satisfactory panting
manoeuvres should be recorded (i.e. a series of almost
superimposed straight lines separated by only a small thermal
drift on the pressure–volume plot; fig. 3), after which the
shutter is opened and the patient performs an ERV manoeuvre,
followed by a slow IVC manoeuvre (or, as a second priority, an
IC manoeuvre followed by a slow EVC manoeuvre). If needed,
the patient can come off the mouthpiece and rest between
TGV/VC manoeuvres. Patients with severe dyspnoea may
have difficulty performing the preferred VC method (i.e. ERV
immediately after TGV, followed by a slow IVC; fig. 2). To
overcome this, the patient can be instructed to take two or
three tidal breaths after the panting manoeuvre, prior to
performing the linked ERV and IVC manoeuvres. 9) For those
unable to perform appropriate panting manoeuvres (e.g. young
children), an alternative is to perform a rapid inspiratory
manoeuvre against the closed shutter. In this situation, it is
essential that the complete rather than the simplified version of
the TGV computation equation [11] is used in the calculation of
TGV. The user should confirm that the complete equation is
used by the computer during such measurements. 10) With
regards to repeatability, at least three FRCpleth values that
agree within 5% (i.e. difference between the highest and lowest
value divided by the mean is f0.05) should be obtained and
the mean value reported. If there is a larger deviation,
additional values should be obtained until three values agree
within 5% of their mean, and the mean value should be
reported.
Quality control
The accuracy of the flow and volume output of the mouth
flow-measuring device should comply with the recommendations made in the spirometry document in this series [20]. The
mouth pressure transducer should be physically calibrated
daily. The plethysmograph signal should also be calibrated
daily, using a volume signal of similar magnitude and
frequency as the respiratory manoeuvres during testing.
A validation of accuracy using a known volume should be
performed periodically. This can be carried out using a
‘‘model’’ lung or container of known volume [11, 26]. Filling
a flask with thermal mass (e.g. copper wool) is essential in
Mouth pressure
plethysmograph by simply occluding the pneumotachograph
orifice, making it adaptable to the respiratory manoeuvre of
interest.
J. WANGER ET AL.
Plethysmograph volume or pressure
FIGURE 3.
Display of a properly performed panting manoeuvre as a series of
almost superimposed straight lines separated by only a small thermal drift.
EUROPEAN RESPIRATORY JOURNAL
J. WANGER ET AL.
STANDARDISATION OF LUNG VOLUME MEASUREMENT
order to simulate the isothermal conditions within the lung;
care should be taken to adjust the calculated volumes to
ambient (or model) temperature and saturated conditions,
rather than to body temperature and ambient pressure,
saturated with water vapour (BTPS) conditions, during the
calculations. The accuracy of adult plethysmographs in
measuring the gas volume of the container should be
¡50 mL or 3%, whichever is greater, based on a mean of five
determinations [11].
At least monthly, or whenever plethysmographic errors are
suspected, two reference subjects (biological controls) should
have their FRCpleth and related RV and TLC measured.
Values that differ significantly (e.g. .10% for FRC and TLC,
or .20% for RV) from the previously established means for
measurements on the same subject suggest errors of measurement. These criteria are approximately twice the reported
coefficients of variation for repeat measurements of these
parameters; hence, tighter standards can be adopted at the cost
of more frequent ‘‘false alarms’’ that suggest equipment
malfunction.
Calculations
The calculation of VTG is based on Boyle’s Law, which states:
Palv1|V TG1~Palv2|V TG2
ð1Þ
Palv1 and VTG1 are the absolute pressure and lung volumes
before the compression/rarefaction manoeuvre, and Palv2 and
VTG2 are the absolute pressure and lung volumes after the
manoeuvre. Water vapour pressure needs to be subtracted
from all pressures, but this is not shown for the sake of
simplicity. Expressed as a change from the baseline, the
equation becomes:
V TG~{(DV=DP)|Palv2
ð2Þ
Since the panting manoeuvre is intended to occur with small
changes in pressure around barometric pressure (PB), the
simplified and widely used version is:
V TG~{(DV=DP)|PB
ð3Þ
volume within the plethysmograph are assumed to be
adiabatic (i.e. there is insufficient time for heat exchange to
occur between the air within the plethysmograph and either
the walls or the subject during the rarefaction and compression
manoeuvre). For panting frequencies in the order of 1 Hz, this
assumption is valid. However, slow rarefaction manoeuvres
where the subject is occluded at end-expiration and the
pressure–volume changes occur with the normal respiratory
effort are to be discouraged, since the time course may allow
for heat exchange within the plethysmograph. This would alter
the pressure–plethysmograph volume calibration. This would
not be a problem if the subject made a rapid inspiratory effort,
but, as mentioned previously, the use of the simplified version
of Boyle’s Law would be inappropriate.
Along the same line, it is customary to subtract the volume of
the apparatus between the mouth and the occluding valve
from the TGV. However, rarefaction and compression of this
volume are not isothermal, and if the volume is large in
relation to TGV due to an excessively large filter, for example,
errors will be introduced. In other words, efforts should be
made to minimise the volume between the occluding valve
and the patient.
MEASUREMENT OF FRC USING NITROGEN WASHOUT
Introduction and theory
This technique is based on washing out the N2 from the lungs,
while the patient breathes 100% O2. The initial alveolar N2
concentration and the amount of N2 washed out can then be
used to calculate the lung volume at the start of washout. The
technique originally utilised gas collections for a 7-min period,
a period deemed adequate for washout of N2 from the lungs of
healthy subjects. The technique has the disadvantage that an
inaccuracy in the measurement of the expired volume or the
final N2 concentration will cause a significant error. The
availability of rapidly responding N2 analysers and computers
has further refined the technique. Additional details and
literature citations regarding various N2 washout techniques
and washout measurements using other gases are available in
a background paper [12].
If the panting manoeuvre begins with a Palv1 that is different
from PB, as occurs if the occlusion takes place at a volume
other than FRC, the volume will need to be corrected to FRC,
but Palv1 will also need to be corrected for PB. Details of the
complete derivation of the equations are given in both a webbased document and background paper [11, 13].
A modification of the 7-min N2 washout method, which
monitors N2 excretion over 5 min and then extrapolates the
late exponential component of the continuous N2 excretion
curve, has been proposed [27], which avoids underestimating
the true alveolar N2 concentration in patients with obstructive
lung disease and eliminates the need for longer washout times.
The current authors are unaware of any commercial pulmonary function testing system that uses this approach; therefore,
manufacturers are encouraged to offer it as an option in the
future. Due to existing variations in currently available
commercial systems and the absence of studies comparing
accuracy, reproducibility and efficiency, no single method for
the measurement of FRC using nitrogen washout (FRCN2) can
be recommended at this time. The following recommendations
are for methods used most commonly in clinical pulmonary
function laboratories.
The underlying assumption of the technique is that the
pressure–volume changes in the body are isothermal, and
any heat generated by compression is instantaneously lost to
the surrounding tissue. However, changes in pressure and
Equipment
N2 analysers should be linear with an inaccuracy f0.2% of full
range throughout the measuring range (0–80%), have a
resolution of f0.01%, and a 95% analyser response time of
EUROPEAN RESPIRATORY JOURNAL
VOLUME 26 NUMBER 3
DV/DP represents the slope of the simultaneous changes in
body volume, which, in a pressure plethysmograph, are the
tiny changes in pressure within the box, calibrated to reflect
changes in the volume of the subject versus the change in
pressure at the mouth. When a rapid inspiratory manoeuvre is
performed, the complete version must be used, as follows:
V TG~{(DV=DP)|Palv2|(Palv1=PB)
ð4Þ
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STANDARDISATION OF LUNG VOLUME MEASUREMENT
If measurements of N2 concentration are made indirectly by
subtracting measurements of O2 and CO2, the accuracy, drift
and linearity characteristics of the O2 and CO2 analysers
should result in indirect calculations of N2, with comparable
performance characteristics to the direct measurements of N2
specified previously. Mass spectrometers should meet the
previously outlined specifications for all three gases, have a
molecular weight resolution of ,1.0, and have ,1% drift over
24 h, or at least be stable for the measurement period after
calibration (which should be carried out immediately before
use).
Pneumotachographs or other flow-measuring devices (e.g.
ultrasonic flow meters, turbines, etc.) incorporated into the
breathing circuits to measure gas flows should comply with
the recommendations from the standardisation of spirometry
document in the present series [20], but they only require a
flow range of 0–6 L?s-1. Factors that must be considered and
controlled to ensure that the previously highlighted performance specifications are met include: the performance characteristics of specific flow-measuring devices; potential
inaccuracies from the condensation of water from expired
gases; changes in gas temperature; and changes in gas viscosity
or density over the range of O2/N2 mixtures.
The system should have a sampling rate of o40 samples?s-1
per channel for flow and N2 signals. Amounts of exhaled N2
should be calculated every 25 ms (or less), with appropriate
corrections for phase differences between flow and N2
measurements [28].
The breathing valve for switching the patient from breathing
room air to 100% O2 should have a dead space ,100 mL for
adults and ,2 mL?kg-1 in smaller children. Oxygen can be
provided either from a gas-impermeable bag filled with dry
100% O2, or a source of O2 connected to a demand valve. As a
result of the effects of inspiratory resistance on FRC, triggering
pressures from demand valves during tidal breathing should
ideally be smaller than those pressures that are acceptable in
IVC manoeuvres occurring during single-breath carbon monoxide diffusing capacity (DL,CO) measurements. This is
especially important in patients with neuromuscular weakness. However, until data that define the magnitude of errors
with lower demand-valve pressures are available, the same
maximal demand-valve pressures that are required for DL,CO
measurements (,1 kPa (,10 cmH20)) are acceptable.
Measurement technique
The measurement technique should adhere to the following
steps. 1) The equipment should be turned on and allowed an
adequate warm-up time, with calibration as instructed by the
manufacturer. 2) The patient should be asked if he/she
has a perforated eardrum (if so, an earplug should be used).
3) The patient is seated comfortably, with no need to remove
dentures. The procedure is explained, emphasising the need to
avoid leaks around the mouthpiece during the washout and
using a nose clip. 4) The patient breathes on the mouthpiece for
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VOLUME 26 NUMBER 3
,30–60 s to become accustomed to the apparatus, and to
assure a stable end-tidal expiratory level. 5) When breathing is
stable and consistent with the end-tidal volume being at FRC,
the patient is switched into the circuit so that 100% O2 is
inspired instead of room air. 6) The N2 concentration is
monitored during the washout. A change in inspired N2 of
.1% or sudden large increases in expiratory N2 concentrations
indicate a leak; hence, the test should be stopped and repeated
after a 15-min period of breathing room air. A typical profile is
shown in figure 4. 7) The washout is considered to be complete
when the N2 concentration is ,1.5% for at least three
successive breaths. 8) At least one technically satisfactory
measurement should be obtained. If additional washouts are
performed, a waiting period of o15 min is recommended
between trials. In patients with severe obstructive or bullous
disease, the time between trials should be o1 h [27]. If more
than one measurement of FRCN2 is made, the value reported
for FRCN2 should be the mean of technically acceptable results
that agree within 10%. If only one measurement of FRCN2 is
made, caution should be used in the interpretation.
Quality control
Before each patient is tested, the N2 analyser should be set to
zero using 100% O2, and then exposed to room air to confirm
calibration. The percentage of N2 for room air should be within
0.5% of the expected reading for room air (i.e. 78.08%). If a
needle valve is used to create a sufficient vacuum to measure
N2 by emission spectroscopy, it should be regularly inspected
and cleaned. Before the initial use and once every 6 months
thereafter, the linearity of the N2 analyser should also be
confirmed by measuring the N2 percentage of a calibration gas
mixture, where the expected N2 concentration is ,40%, either
from a certified calibration tank or created using precision
dilution techniques. Observed values should be within 0.5% of
expected, and readings must be corrected for nonlinearity
greater than this.
The accuracy of the flow and volume output of the flowmeasuring device should be confirmed at least daily with a
calibrating syringe, using pumping frequencies that will result
N2 fraction %
,60 ms to a 10% step change in N2 concentration (after
correction for phase shift). Compliance with these performance
specifications should be confirmed by the manufacturers, since
few clinical laboratories have the resources required for such
evaluations [13].
J. WANGER ET AL.
Total volume washed out
FIGURE 4.
Display of a normal profile of a multiple-breath N2 washout with the
patient breathing 100% O2. The area under the curve is the N2 volume washed out,
which, divided by the total volume washed out, gives the fractional concentration of
N2 in the volume of gas washed out at the end of the test or in the end-tidal gas of
the last breath at the end of the test.
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J. WANGER ET AL.
STANDARDISATION OF LUNG VOLUME MEASUREMENT
in flows of the same range as tidal flows, and should comply
with the recommendations made in a previous document in
this series [20]. Initially and monthly, exhalation volumes
should be checked with the syringe filled with room air, and
inhalation volumes with the syringe filled with 100% O2. The
temperature should be validated as described previously [19].
Testing of biological controls should be performed at least
monthly.
Calculations
FRCN2 is computed from the following equation:
FRCN2 |FN2 1~(FRCN2 |FN2 2zN2 volume washed out)
{(N2 volume from tissue)
ð5Þ
Solving for FRCN2, this becomes:
FRCN2 ~(N2 volume washed out
N2 volume from tissue)=(FN2 1{FN2 2)
ð6Þ
where FN21 and FN22 are the fractions of N2 in the end-tidal gas
before the washout, and in the end-tidal gas of the last breath
at the end of the test, respectively. The N2 volume washed out
is the volume in the bag multiplied by the N2 fraction of the
mixed gas in the bag, or it is calculated on-line as the sum of
FN26VT for all the breaths, with FN2 being the mixed expired
fraction of N2 in the individual breath and VT the volume of
that breath. This sum equals the area under the curve in
figure 4. This value of FRCN2 should be corrected to BTPS
conditions, and the volume of the equipment dead space must
be subtracted.
N2 excreted from the tissues can be estimated from tables or
complex exponential equations. Since the difference in the
correction when these different sources are used is small, it is
recommended that the following relatively simple equation for
estimating tissue excretion, adjusted for body size as a result of
N2 eliminated after a 7-min washout period, is used [29]. As
the largest fraction of the N2 is excreted in the first phase of the
washout, this equation can be assumed to be appropriate for
washout times of ,7 min:
N2 tissue excretion (mL)~((BSA|96:5)z35)=0:8
ð7Þ
where BSA is the body surface area in m2, and is determined
by using weight in kg and height in cm in the following
equation [30]:
BSA~0:007184|weight0:425 |height0:725
ð8Þ
MEASUREMENT OF FRC USING HELIUM DILUTION
Introduction and theory
The method for measuring lung volumes is based on the
equilibration of gas in the lung with a known volume of gas
containing helium [31, 32]. The test gas consists of air with
added oxygen of 25–30%, but higher concentrations are
acceptable. Helium is added to a concentration of ,10% (full
scale) [9]. The lung volume (FRCHe) at the time the subject is
connected to the spirometry apparatus of a known volume
(Vapp) and helium fraction (FHe1) is calculated from the helium
EUROPEAN RESPIRATORY JOURNAL
fraction at the time of equilibration (FHe2) as follows:
V app|FHe1~(V appzFRCHe)|(FHe2)
ð9Þ
FRCHe~V app(FHe1{FHe2)=FHe2
ð10Þ
where lung volume includes the dead space of the valve and
mouthpiece, which must be subtracted, and FRCHe should be
corrected to BTPS conditions.
Equipment
For systems that utilise a volume-displacement spirometer, the
capacity of the spirometer should be o7 L. It should be noted,
however, that the larger the spirometer is, the higher is the
required resolution of the helium measurements. The specifications for the volume measurements should comply with the
recommendations in a previous document in this series [20].
Furthermore, the Vapp with the bell at zero volume, including
the circuit tubing to the mouthpiece valve, should not exceed
4.5 L, since the smaller the Vapp is at the time that the patient is
switched into the circuit, the larger (and more accurate) the
measured changes in helium concentration during the FRC
measurement will be.
The spirometer should be equipped with a mixing fan, CO2
absorber, O2 and helium supply, a gas inlet and outlet, and a
water vapour absorber in the line to the helium analyser.
Before the measurements, enough 100% helium should be
added to the system to give a helium reading of ,10%. The
remainder of the gas added to the system can be room air or a
mixture of room air and O2. If room air is used, it is important
to ensure adequate O2 replacement during the test. The mixing
fan should mix the gas throughout the circuit within 8 s after
the end of exhalation into the circuit. Typically, breathingcircuit flows of ,50 L?min-1 are utilised to ensure adequate
mixing of helium concentration measurements, which are
reported every 15 s. If pneumotachometers or other flow
devices are used instead of volume-displacement spirometers,
and if they are not isolated from variations in gas properties
(e.g. by bag-in-box systems), then appropriate calibrations and
corrections may be necessary to accommodate the changes in
gas properties.
A thermal-conductivity helium analyser is the type utilised
most commonly, but other types of helium analysers may be
used [33]. The helium analyser should have a range of ,0–10%
helium, a resolution of f0.01% helium over the entire range,
and a 95% response time of ,15 s to a 2% step change in
helium concentration in the breathing circuit. The meter
should be stable with a drift of f0.02% for measurement
periods of up to 10 min. For systems in which O2 concentration
changes substantially because of O2 consumption during the
measurement of FRC, the helium analyser must be calibrated
over the range of O2 concentrations encountered. Since
thermal-conductivity helium analysers are sensitive to temperature changes, it should be ensured that the temperature of
the gases entering the helium analyser is the same as that
during calibration.
A small pump samples gas from the breathing circuit just
beyond the CO2 absorber, and pushes it through a desiccant
chamber, through the helium analyser and back into the main
VOLUME 26 NUMBER 3
517
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STANDARDISATION OF LUNG VOLUME MEASUREMENT
The breathing valve and mouthpiece should have a combined
dead space of ,100 mL, and should be easy to disassemble for
sterilisation. The size of this dead space should be available
from the manufacturer or measured by water displacement.
Continuous measurement of the O2 concentration ensures a
satisfactory O2 supply and also provides a means to adjust the
output of thermal-conductivity helium analysers for the effect
of different O2 concentrations.
Measurement technique
Specific details of procedures will vary with different types of
equipment and degrees of automation [9], but the basic
procedure is as follows. 1) The equipment should be turned
on and allowed an adequate warm-up time. 2) The equipment
should be set up for testing, including calibration, according to
manufacturer’s instructions. 3) The patient should be asked if
he/she has a perforated eardrum (if so, an earplug should be
used). 4) The patient is seated comfortably, with no need to
remove dentures. The procedure is explained, emphasising the
need to avoid leaks around the mouthpiece during the test and
to use a nose clip. 5) The patient breathes for ,30–60 s on the
mouthpiece to become accustomed to the apparatus, and to
ensure a stable end-tidal expiratory level. 6) The patient is
turned ‘‘in’’ (i.e. connected to the test gas) at the end of a
normal tidal expiration. 7) The patient is instructed to breathe
regular tidal breaths. 8) The O2 flow is adjusted to compensate
for O2 consumption (significant errors in the calculation of FRC
can result if O2 consumption is not adequately accounted for).
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VOLUME 26 NUMBER 3
Quality control
Before each patient is tested, the following items should be
checked: water level of water-sealed spirometers (if applicable); status of all CO2 and water absorbers; operation of the
circuit fan (assessed by listening); and the baseline stability of
helium and volume signals. Systems that can be pressurised
conveniently (e.g. by placing a weight on top of an upright
a)
Helium
concentration
Lung volumes are reported at BTPS conditions. When TLC and
subdivisions thereof are measured, the temperature of gas
inside the system differs from both BTPS and the ambient
temperature and pressure, saturated with water vapour
(ATPS) conditions computed using room temperature, since
the conditions are variably affected by exhaled warm gas,
room temperature, and heat generated by absorption of CO2 in
the soda lime canister. Therefore, the temperature of the gas in
the breathing circuit should be measured so that these lung
volumes can be corrected to BTPS conditions. The temperature
sensor should have an accuracy of better than 0.5 ˚C over the
range of 12–30 ˚C, and should have a 90% response time of
,30 s to a 5 ˚C step change of temperature of the gas inside the
breathing circuit.
9) The helium concentration is noted every 15 s. 10) Helium
equilibration is considered to be complete when the change in
helium concentration is ,0.02% for 30 s. The test rarely
exceeds 10 min, even in patients with severe gas-exchange
abnormalities [9]. 11) Once the helium equilibration is
complete, the patient is turned ‘‘out’’ (i.e. disconnected from
the test gas) of the system. If the measurements of ERV and IC
are to be linked to the FRC measured, it should be ensured that
the spirometer has an adequate volume for the full ERV and
IVC manoeuvres (fig. 5). 12) At least one technically satisfactory measurement should be obtained. Due to the extra costs
and time in making multiple measurements, and the relatively
good inter-day variability in adults, two or more measurements of FRCHe need to be made only when necessitated by
clinical or research need [9]. If only one measurement of FRCHe
is made, caution should be used in the interpretation. For
younger children, however, it is recommended that at least two
technically satisfactory measurements be performed. If more
than one measurement of FRCHe is carried out, the value
reported for FRCHe should be the mean of technically
acceptable results that agree within 10%.
FHe1
FHe2
b)
IC
Volume
circuit; for most analysers, a flow of o200 mL?min-1 is
necessary. Since changes in the flow of gas through the
analyser or in the pressure of gas in the analyser circuit will
affect response time or accuracy, variations in flow and
pressure should be minimised. Similarly, since thermalconductivity analysers also respond to changes in concentration of CO2, O2, N2 and water vapour pressure, CO2 and water
are removed before the sample is introduced into the helium
analyser, and the O2 concentration is maintained relatively
constant by adding O2 to the circuit as necessary. The activity
of the CO2 and water absorbers should be ensured before each
test (either from visual or photocell detection of indicator
colour changes, or by replacing the absorbent after a specified
number of tests (or accumulated minutes of equilibration
time)). The breathing-circuit CO2 level during testing should
be kept below 0.5% to avoid patient discomfort and hyperventilation.
J. WANGER ET AL.
IRV
VT
ERV
FRC
Patient switched
into the system,
or FHe1
FIGURE 5.
Patient switched
out of the system,
or FHe2
Time
RV
Display of an acceptable profile for a helium dilution test to
determine functional residual capacity (FRC), in which O2 is continually added to
compensate for O2 consumption. As the helium concentration falls (a), it
corresponds to the time course of the volume change (b). To obtain ‘‘linked’’
expiratory reserve volume (ERV) and inspiratory vital capacity manoeuvres, the
patient should not be switched out of the system as shown. FHe1: helium fraction at
the time that the subject is connected to the apparatus; FHe2: helium fraction at the
time of equilibration; IC: inspiratory capacity; IRV: inspiratory reserve volume; VT:
tidal volume (TV); RV: residual volume.
EUROPEAN RESPIRATORY JOURNAL
J. WANGER ET AL.
It is necessary to check the linearity of the helium meter
periodically or when erroneous results are suspected. This is
accomplished by diluting a measured helium concentration
with known volumes of air (maximum error of 0.5% of full
scale, which would be 0.05% for 10% helium). However,
contemporary helium meters have very stable linearity. If the
stability of the helium meter linearity has been demonstrated
(e.g. by weekly checks over a few months), then quarterly or
semi-annual checks seem sufficient, as there are no available
data to support more frequent linearity checks for all
instruments. Monthly testing of biological controls is recommended and useful, in that it tests not only the equipment, but
also the procedures used by the technicians.
Calculations
Providing the subject is connected to the spirometer at FRC,
FRCHe can be calculated from the previously stated equations
(included in the introduction and theory of the measurement
of FRC using helium dilution).
With regards to corrections in calculating FRCHe, the following
points should be considered. 1) FRCHe is determined at a
condition between ATPS and BTPS, and should be corrected to
BTPS. 2) It is recommended that no corrections for helium
absorption be made. 3) Correction factors for N2 excretion
during the helium equilibration, and corrections for helium
concentration when the respiratory quotient differs from 1.0
can be ignored [9]. 4) With regards to switching errors, in
practice, patients are not always at FRC when they are
switched into the spirometer circuit. Corrections for this
should be made from the spirometer trace when reporting
FRCHe (fig. 6). Some computerised systems report and account
for the switch-in error automatically, but it is still preferable for
continuous recordings of spirometry to be available so the
computer-derived adjustments for switch-in errors can be
confirmed by the technologist.
Volume
DV
FRC
b)
Volume
The stability of the helium meter should be confirmed weekly
(it should not drift .0.02% in 10 min). The temperature should
be validated as described previously [19].
a)
DV
FRC
c)
Volume
water-sealed spirometer) should be checked for leaks at least
once during the 24 h prior to patient testing, and after tubing
or canister changes.
STANDARDISATION OF LUNG VOLUME MEASUREMENT
DV
FRC
Time
FIGURE 6.
Display of volume–time spirograms, showing examples when
the patient is not switched into the spirometer circuit. a) The patient was turned into
the circuit at a lung volume higher than the functional residual capacity (FRC), and
the volume difference (DV) would be subtracted. b) The patient is turned into the
circuit at a lung volume below FRC, and the DV would be added. c) The patient was
turned into the circuit above the true FRC, and the DV would be subtracted.
Modified from [16].
planimeters in order to derive the confined volume.
Adjustments are made for magnification factors, volumes of
the heart, the intrathoracic tissue and blood, and infradiaphragmatic spaces. In the determination of TLC, 6–25% of
subjects differed by .10% from plethysmographic measurements in adult subjects [34]. For paediatric applications,
studies are more problematic [35].
MEASUREMENT OF LUNG VOLUMES USING IMAGING
TECHNIQUES
In subjects with a limited ability to cooperate, radiographic
lung volumes may be more feasible than physiological
measurements. The definition of the position of lung inflation
at the time of image acquisition is clearly essential. Volumes
measured this way carry their own assumptions and limitations, and cannot be directly compared with volumes
measured by the techniques mentioned previously. Imaging
techniques for use in children and adults have been reviewed
in a previous report [4], from where the following information
is derived.
Computed tomography
In addition to thoracic cage volumes, CTs can provide
estimates of lung tissue and air volumes, and can also estimate
the volume of lung occupied by increased density (e.g. in
patchy infiltrates) or decreased density (e.g. in emphysema or
bullae). In a study of children, comparable correlations were
observed for CT and radiographic measurements as compared
with plethysmographic TLC [36–38]. A disadvantage of using
CT is the high radiation dose. This dose can probably be
considerably diminished by modifying the technique.
Conventional radiographs
The principle is to outline the lungs in both anteroposterior
and lateral chest radiographs, and determine the outlined
areas either by assuming a given geometry or by using
Magnetic resonance imaging
Magnetic resonance imaging (MRI) offers the advantage of a
large number of images within a short period of time, so that
volumes can be measured within a single breath. As with CT,
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STANDARDISATION OF LUNG VOLUME MEASUREMENT
MRI offers the potential for scanning specific regions of the
lung, as well as the ability to adjust for lung water and tissue.
However, despite the advantages of an absence of radiation
exposure, the use of MRI for measuring thoracic gas volume
will be limited by its considerable cost.
Controversies and critical questions
There are inadequate data in the literature to support
recommending one specific technique over the other, or to
standardise imaging techniques for measurement of thoracic
gas volumes. It is a question of whether TLC values obtained
during routine chest radiographs are sufficiently close to those
achieved in pulmonary function laboratories. A few studies
indicate that radiographic TLC is slightly smaller than the
latter [39, 40], but this may relate to a lack of proper coaching
in enabling the patient to reach TLC during the radiographic
procedure. The larger standard deviations of radiographic
measurements may limit their clinical usefulness. In patients
with lung disease, the difference between radiographic
measurements and lung function measurements may be due
to differences in the ability to include airspace-occupying
tissue, leading to a tendency for the radiographic method to
give higher values. CT and MRI techniques offer the potential
for measuring intrathoracic volumes and estimating lung gas
volumes after subtraction of estimates of fluid and tissue
volumes derived from measurements of image density.
REFERENCE VALUES
Lung volumes are related to body size, with standing height
being the most important factor. In children and adolescents,
lung growth appears to lag behind the increase in standing
height during the growth spurt, and there is a shift in
relationship between the lung volume and height during
adolescence [41, 42].
A number of factors must be considered when selecting
predictive values for absolute lung volumes including: matching of the reference and patient populations; appropriate
extrapolation of regression equations, when considering the
size and age range of subjects actually studied; and differences
in testing methodology between clinical laboratories and
studies from which predicted reference values are derived.
Additional information is provided elsewhere [1].
INFECTION CONTROL
This subject is discussed in more detail in a previous document
from this series [19].
ABBREVIATIONS
Table 1 contains a list of abbreviations and their meanings,
which will be used in this series of Task Force reports.
TABLE 1
ATPD
List of abbreviations and meanings
Ambient temperature, ambient pressure, and dry
ATPS
Ambient temperature and pressure saturated with water vapour
BTPS
Body temperature (i.e. 37˚C), ambient pressure, saturated with
water vapour
C
Centigrade
CFC
Chlorofluorocarbons
cm
Centimetres
520
VOLUME 26 NUMBER 3
J. WANGER ET AL.
TABLE 1
(Continued)
COHb
Carboxyhaemoglobin
DL,CO
Diffusing capacity for the lungs measured using carbon
DL,CO/VA
Diffusing capacity for carbon monoxide per unit of alveolar
DM
Membrane-diffusing capacity
monoxide, also known as transfer factor
volume, also known as KCO
DT
Dwell time of flow .90% of PEF
EFL
Expiratory flow limitation
ERV
Expiratory reserve volume
EV
Back extrapolated volume
EVC
Expiratory vital capacity
FA,X
Fraction of gas X in the alveolar gas
FA,X,t
Alveolar fraction of gas X at time t
FEF25–75%
Mean forced expiratory flow between 25% and 75% of FVC
FEFX%
Instantaneous forced expiratory flow when X% of the FVC has
FEV1
Forced expiratory volume in one second
FEVt
Forced expiratory volume in t seconds
FE,X
Fraction of expired gas X
FIFX%
Instantaneous forced inspiratory flow at the point where X% of
FI,X
Fraction of inspired gas X
FIVC
Forced inspiratory vital capacity
FRC
Functional residual capacity
been expired
the FVC has been inspired
FVC
Forced vital capacity
H2 O
Water
Hb
Haemoglobin
Hg
Mercury
Hz
Hertz; cycles per second
IC
Inspiratory capacity
IRV
Inspiratory reserve volume
IVC
Inspiratory vital capacity
KCO
Transfer coefficient of the lung (i.e. DL,CO/VA)
kg
Kilograms
kPa
Kilopascals
L
Litres
L?min-1
Litres per minute
L?s-1
Litres per second
lb
Pounds weight
MEFX%
Maximal instantaneous forced expiratory flow where X% of the
MFVL
Maximum flow–volume loop
mg
Milligrams
MIF
Maximal inspiratory flow
mL
Millilitres
mm
Millimetres
MMEF
Maximum mid-expiratory flow
ms
Milliseconds
MVV
Maximum voluntary ventilation
PA,O2
Alveolar oxygen partial pressure
PB
Barometric pressure
PEF
Peak expiratory flow
PH2O
Water vapour partial pressure
PI,O2
Inspired oxygen partial pressure
h (theta)
Specific uptake of CO by the blood
RT
Rise time from 10% to 90% of PEF
RV
Residual volume
s
Seconds
FVC remains to be expired
EUROPEAN RESPIRATORY JOURNAL
J. WANGER ET AL.
STANDARDISATION OF LUNG VOLUME MEASUREMENT
The original ATS/NHLBI Workshop participants (and their
affiliations at the time when the workshop was convened)
were as follows: E. Bancalari (University of Miami, Miami, FL,
USA); R.A. Brown (Massachusetts General Hospital, Boston,
MA, USA); J.L. Clausen (University of California, San Diego,
CA, USA); A.L. Coates (Hospital for Sick Children, Toronto,
Canada); R. Crapo (LDS Hospital, Salt Lake City, UT, USA); P.
Enright (University of Arizona, Tucson, AZ, USA); C. Gaultier
(Hopital Robert Debre, Paris, France); J. Hankinson (NIOSH,
Morgantown, WV, USA); R.L. Johnson Jr (University of Texas,
Dallas, TX, USA); D. Leith (Kansas State University,
Manhattan, KS, USA); C.J.L. Newth (Children’s Hospital, Los
Angeles, CA, USA); R. Peslin (Vandoeuvre Les Nancy, France);
P.H. Quanjer (Leiden University, Leiden, The Netherlands); D.
Rodenstein (Cliniques St. Luc, Brussels, Belgium); J. Stocks
(Institute of Child Health, London, UK); and J-C. Yernault{
(Hospital Erasme, Brussels, Belgium).
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EUROPEAN RESPIRATORY JOURNAL
VOLUME 26 NUMBER 3
TABLE 1
(Continued)
STPD
Standard temperature (273 K, 0˚C), pressure (101.3 kPa,
TB
Tuberculosis
760 mmHg) and dry
TGV (or VTG)
Thoracic gas volume
tI
Time taken for inspiration
TLC
Total lung capacity
Tr
Tracer gas
ttot
Total time of respiratory cycle
TV (or VT)
Tidal volume
VA
Alveolar volume
VA,eff
Effective alveolar volume
VC
Vital capacity
Vc
Pulmonary capillary blood volume
VD
Dead space volume
VI
Inspired volume
VS
Volume of the expired sample gas
mg
Micrograms
ACKNOWLEDGEMENTS
J. Wanger: Pharmaceutical Research Associates, Inc., Lenexa,
KS, USA; J.L. Clausen: University of California, San Diego, CA,
USA; A. Coates: Hospital for Sick Children, Toronto, ON,
Canada; O.F. Pedersen: University of Aarhus, Aarhus,
Denmark; V. Brusasco: Università degli Studi di Genova,
Genova, Italy; F. Burgos: Hospital Clinic Villarroel, Barcelona,
Spain; R. Casaburi: Harbor UCLA Medical Center, Torrance,
CA, USA; R. Crapo and R. Jensen: LDS Hospital, Salt Lake City,
UT, USA; P. Enright: 4460 E Ina Rd, Tucson, AZ, USA; C.P.M.
van der Grinten: University Hospital of Maastricht, Maastricht,
the Netherlands; P. Gustafsson: Queen Silvias Children’s
Hospital, Gothenburg, Sweden; J. Hankinson: Hankinson
Consulting, Inc., Valdosta, GA, USA; D.C. Johnson:
Massachusetts General Hospital and Harvard Medical School,
Boston, MA, USA; N. MacIntyre: Duke University Medical
Center, Durham, NC, USA; R. McKay: Occupational Medicine,
Cincinnati, OH, USA; M.R. Miller: University Hospital
Birmingham NHS Trust, Birmingham, UK; D. Navajas:
Universitat de Barcelona – IDIBAPS, Barcelona, Spain; R.
Pellegrino: Azienda Ospedaliera S. Croce e Carle, Cuneo, Italy;
G. Viegi: CNR Institute of Clinical Physiology, Pisa, Italy.
521
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